Turbine bypass desuperheater control system

Abstract

An adaptive control system for controlling the temperature of desuperheated steam in a turbine bypass system. In one embodiment of the invention, redundant temperature sensors downstream of desuperheating water sprays provide an indication of the actual steam temperature after desuperheating has occurred. The highest value of temperature is automatically selected for control and to provide an error signal to a controller. The controller output, indicative of the deviation from a desired temperature, is multiplied by a factor proportional to steam flow in the bypass system. The multiplied signal is then utilized to proportionally position one or more water control valves to spray more or less water into the bypassed steam. The control system thus automatically adapts itself to variations in steam flow. Preferably, the steam flow is taken as the product of the position of a steam flow throttling valve in the bypass line and the steam supply pressure ahead of the valve. Additionally, operating parameters such as temperature and differential pressures are monitored and continuously compared against limiting values to provide automatic protection action if any of the conditions being monitored warrant such action.

What is claimed is: 
     
       1. In combination with a steam turbine having a bypass system for diverting excess steam supplied by a steam generator from the turbine and including means for desuperheating the bypassed steam and at least one steam flow control valve, a steam desuperheater control system for controlling the temperature of desuperheated steam, comprising: temperature determining means providing a representation of the temperature of the desuperheated steam;   first control means operatively connected to said desuperheating means and responsive to said temperature representation to provide corrective action to said desuperheating means tending to maintain the temperature of the desuperheated steam at a preselected temperature reference value;   steam flow determining means providing a representation of steam flow rate in said bypass subsystem; and   second control means responsive to said steam flow representation and interactive with said first control means to alter said corrective action as a function of steam flow rate in said bypass subsystem.   
     
     
       2. The combination of claim 1 wherein said steam flow determining means is a multiplier providing said steam flow representation as the product of steam pressure being supplied to said bypass system and the degree of opening of said steam flow control valve. 
     
     
       3. The combination of claim 1 wherein said second control means is a multiplier adapted to alter the corrective action of said first control means by a factor proportional to said flow representation. 
     
     
       4. The combination of claim 2 wherein said second control means is a multiplier altering the corrective action of said first control means by a factor proportional to said steam flow representation. 
     
     
       5. The combination of claims 1, 2, 3, or 4 wherein said control system includes a protection subsystem responsive to bypass system operating parameters in excess of preselected values thereof by providing protective action operative to control excessive steam temperatures and liquid water induction in said bypass system. 
     
     
       6. The combination of claim 5 wherein said temperature determining means is redundantly provided and said control system further includes; a high-value selector for automatically selecting the highest value of redundantly provided representations of steam temperature;   a default temperature reference representing a preselected steam temperature value;   a temperature selector responsive to said protection subsystem to automatically select said highest value representation of temperature or said default temperature as demanded by said protective action.   
     
     
       7. The combination of claim 6 wherein said protection subsystem includes; a temperature sensing switch providing a first response to a preselected high temperature of desuperheated steam and a second response to a preselected low temperature of desuperheated steam;   a valve position sensor responsive to the degree of opening of said steam flow control valve to provide a signal indicative that said valve is open in excess of a preselected amount; and   logic means for rapidly closing said steam flow control valve whenever said first response is received and said steam flow control valve is open in excess of said preselected amount or whenever said second temperature response is received.   
     
     
       8. The combination of claim 7 wherein said protection subsystem includes; means providing a representation of differential steam pressure between a first steam path location and a second steam path location; and   logic means for selecting said default temperature whenever said differential pressure representation exceeds a preselected reference value.   
     
     
       9. An adaptive control system for controlling the desuperheating of steam flowing in the steam bypass system of a steam turbine and wherein said bypass system includes a steam flow control valve, said control system comprising: spraying means to spray liquid water into said bypass flow of steam to provide desuperheating thereof;   means responsive to a control signal to adjust the water flow rate to said spraying means;   temperature sensing means downstream of said water spray means providing a temperature signal indicative of the temperature of desuperheated steam;   first control means responsive to said temperature signal to produce a corrective signal tending to cause said water flow adjust means to adjust water flow in a manner tending to maintain a preselected temperature of desuperheated steam;   steam flow sensing means providing a signal indicative of desuperheated steam flow rate; and   second control means responsive to said steam flow rate signal and to said corrective signal to produce said water adjust control signal as the product of said steam flow rate signal and said corrective signal.   
     
     
       10. The control system of claim 9 wherein said steam flow sensing means comprises a multiplier providing said signal indicative of desuperheated steam flow rate as the produce of a signal representative of pressure of steam supplied to said bypass system and a signal representative of the degree of opening of said steam flow control valve. 
     
     
       11. The control system of claim 9 or claim 10 wherein said control system further includes a protection subsystem responsive to bypass system operating parameters in excess of preselected values or said parameters by providing protective action operative to control excessive steam temperature and liquid water induction in said bypass system.